U.S. patent number 11,110,929 [Application Number 16/347,224] was granted by the patent office on 2021-09-07 for anti-skid control device for vehicle.
This patent grant is currently assigned to ADVICS CO., LTD.. The grantee listed for this patent is ADVICS CO., LTD.. Invention is credited to Yohei Mizuguchi, Masato Terasaka.
United States Patent |
11,110,929 |
Mizuguchi , et al. |
September 7, 2021 |
Anti-skid control device for vehicle
Abstract
Anti-skid control is performed by switching between a reduction
mode for reducing braking torque and an increase mode for
increasing braking torque based on a comparison between four wheel
speeds and vehicle body speed. A controller calculates wheel
accelerations based on wheel speeds and includes a control mode
condition where the reduction mode is selected at each wheel and a
wheel acceleration condition where each wheel acceleration is
within a predetermined value range. If a state in which the control
mode condition and the wheel acceleration condition are
simultaneously satisfied is maintained over a predetermined time
period, the controller determines that a residual state is
satisfied. When the residual state is not satisfied, the controller
calculates vehicle body speed based on the maximum value of the
wheel speeds, whereas when the residual state is satisfied, the
controller calculates vehicle body speed based on the minimum value
of the wheel speeds.
Inventors: |
Mizuguchi; Yohei (Kariya,
JP), Terasaka; Masato (Ichinomiya, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
ADVICS CO., LTD. |
Kariya |
N/A |
JP |
|
|
Assignee: |
ADVICS CO., LTD. (Kariya,
JP)
|
Family
ID: |
1000005791835 |
Appl.
No.: |
16/347,224 |
Filed: |
November 10, 2017 |
PCT
Filed: |
November 10, 2017 |
PCT No.: |
PCT/JP2017/040566 |
371(c)(1),(2),(4) Date: |
May 03, 2019 |
PCT
Pub. No.: |
WO2018/088514 |
PCT
Pub. Date: |
May 17, 2018 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20190256099 A1 |
Aug 22, 2019 |
|
Foreign Application Priority Data
|
|
|
|
|
Nov 11, 2016 [JP] |
|
|
JP2016-220102 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60W
30/18109 (20130101); B60T 8/171 (20130101); B60T
8/32 (20130101); B60T 8/1761 (20130101); B60W
30/18172 (20130101); B60W 40/105 (20130101); B60W
2520/10 (20130101); B60W 2520/28 (20130101); B60W
2520/26 (20130101) |
Current International
Class: |
B60W
40/105 (20120101); B60W 30/18 (20120101); B60T
8/171 (20060101); B60T 8/32 (20060101); B60T
8/1761 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
International Search Report (PCT/ISA/210) dated Feb. 13, 2018, by
the Japan Patent Office as the International Searching Authority
for International Application No. PCT/JP2017/040566. cited by
applicant .
Written Opinion (PCT/ISA/237) dated Feb. 13, 2018, by the Japan
Patent Office as the International Searching Authority for
International Application No. PCT/JP2017/040566. cited by
applicant.
|
Primary Examiner: Nolan; Peter D
Assistant Examiner: Redhead, Jr.; Ashley L
Attorney, Agent or Firm: Buchanan Ingersoll & Rooney
PC
Claims
The invention claimed is:
1. An anti-skid control device for a vehicle applied to a four
wheel drive vehicle in which a driving force from a driving source
of the vehicle is transmitted to four wheels, the anti-skid control
device comprising: a wheel speed sensor that detects wheel speeds
of four wheels of the vehicle; and a controller that calculates a
vehicle body speed of the vehicle based on at least one of the four
wheel speeds and executes an anti-skid control for suppressing lock
tendency of the four wheels by selectively switching between a
reduction mode of reducing a braking torque applied to the four
wheels and an increase mode of increasing the braking torque based
on a comparison result between the four wheel speeds and the
vehicle body speed; wherein the controller calculates accelerations
of the four wheels based on the four wheel speeds, and is
configured to include a control mode condition of selecting the
reduction mode in all of the four wheels and a wheel acceleration
condition in which the accelerations of all of the four wheels are
within a range of a predetermined wheel acceleration; the
controller determines as a residual state when a state in which the
control mode condition and the wheel acceleration condition are
satisfied at the same time is continued for a predetermined time,
calculates the vehicle body speed based on a maximum speed value,
which is a maximum value of the four wheel speeds, when determined
as not the residual state, and calculates the vehicle body speed
based on a minimum speed value, which is a minimum value of the
four wheel speeds, when determined as the residual state.
2. The anti-skid control device for the vehicle according to claim
1, wherein the controller is configured to include a wheel speed
condition in which a difference between the maximum speed value and
the minimum speed value is less than or equal to a predetermined
speed; and the controller determines as the residual state when a
state in which the control mode condition, the wheel acceleration
condition, and the wheel speed condition are satisfied at the same
time is continued for the predetermined time.
3. An anti-skid control device for a vehicle applied to a four
wheel drive vehicle in which a driving force from a driving source
of the vehicle is transmitted to four wheels, the anti-skid control
device comprising: a wheel speed sensor that detects wheel speeds
of four wheels of the vehicle; and a controller that calculates a
vehicle body speed of the vehicle based on at least one of the four
wheel speeds and executes an anti-skid control for suppressing lock
tendency of the four wheels by selectively switching between a
reduction mode of reducing a braking torque applied to the four
wheels and an increase mode of increasing the braking torque based
on a comparison result between the four wheel speeds and the
vehicle body speed; wherein the controller is configured to include
a control mode condition of selecting the reduction mode in all of
the four wheels and a wheel speed condition in which a difference
between a maximum speed value, which is a maximum value of the four
wheel speeds, and a minimum speed value, which is a minimum value
of the four wheel speeds, is less than or equal to a predetermined
speed; and the controller determines as a residual state when a
state in which the control mode condition and the wheel speed
condition are satisfied at the same time is continued for a
predetermined time, calculates the vehicle body speed based on the
maximum speed value when determined as not the residual state, and
calculates the vehicle body speed based on the minimum speed value
when determined as the residual state.
Description
TECHNICAL FIELD
The present invention relates to an anti-skid control device for a
vehicle.
BACKGROUND ART
Patent literature 1 describes, in an aim of "providing an anti-skid
control device in a four wheel drive vehicle that can prevent
erroneous judgment at the time of traveling on a rough road or the
like and reliably detect drive system vibration, so that occurrence
of troubles such as missing of deceleration, insufficient
deceleration, increase in braking stop distance, and the like due
to erroneous judgment can be prevented while allowing the execution
of a drive system vibration convergence process only at the time of
occurrence of the drive system vibration", "calculating an absolute
value of a difference between an average value VWDFA of wheel
accelerations VWDFL, VWDFR of the left and right front wheels 14,
10 and an average value of wheel accelerations VWDRL, VWDRR of the
left and right rear wheels 22, 20 as DVWD_FR
(=|VWDFA-VWDRA|)VWDFA-VWDRA|), and judging that the drive system
vibration occurred when such acceleration difference DVWD_FR
exceeds a vibration judgment approach threshold value DVWDVIB#.
In the anti-skid control device for the four-wheel drive vehicle,
there is a problem caused not only by the above-described drive
system vibration but also by the acceleration slip. This will be
described with reference to a time series diagram of FIG. 4. In
FIG. 4, a situation where sudden braking is performed immediately
after the vehicle is rapidly accelerated, and the antiskid control
is started is assumed.
Until time point t0, the vehicle is rapidly accelerated, and a
wheel speed Vwa [**] is increased. Since the wheel speed Vwa [**]
includes an acceleration slip Sks, the wheel speed Vwa [**] is
larger than a true value Vxs of a vehicle body speed. Due to the
acceleration slip Sks, the vehicle body speed Vxa estimated from
the wheel speed Vwa [**] becomes a value larger than its true value
Vxs. Here, when the wheel speed Vwa [**] matches the true value Vxs
of the vehicle body speed, neither the acceleration slip Sks nor
the deceleration slip Sgn is included in the wheel speed Vwa
[**].
At time point t0, the driver releases the foot from the accelerator
pedal, and the acceleration operation is ended. Then, at time point
t1 immediately thereafter, an abrupt braking operation is started.
Due to such sudden braking, the anti-skid control is started at
time point t2.
Since the wheel WH [**] is connected to a power source PWU through
a transmission TRN, the influence of acceleration still remains. In
addition, in a four-wheel drive vehicle, since the wheel WH [**] is
mechanically connected to the power source PWU and the transmission
TRN, its moment of inertia is relatively large. Therefore, after
the time point t2 at when the anti-skid control is started, the
speed Vwa [**] of each wheel WH [**] is gradually reduced toward
the true value Vxs of the vehicle body speed while the influence of
acceleration remains.
In the anti-skid control, the vehicle body speed Vxa is determined
based on the fastest of the four wheel speeds Vwa [**]. Therefore,
the maximum value of the wheel speed Vwa [**] is adopted for the
determination of the vehicle body speed Vxa. As a result, the
vehicle body speed Vxa is calculated to have a relatively large
value.
In the anti-skid control, the slip state quantity Slp [**] is
calculated based on the difference between the wheel speed Vwa [**]
and the vehicle body speed Vxa. Then, a braking torque (i.e., wheel
cylinder hydraulic pressure) is adjusted based on the slip state
quantity Slp [**]. Therefore, when the vehicle body speed Vxa is
determined to be relatively large, the slip state quantity Slp is
determined to be large, and the braking torque is easily reduced.
That is, due to the influence of the acceleration slip Sks
remaining in the wheel speed Vwa [**], the braking torque may be
reduced more than necessary in the anti-skid control.
As described above, in the anti-skid control device for a vehicle
applied to a four-wheel drive vehicle, it is desired that an
influence of the acceleration slip Sks is compensated and a vehicle
body speed Vxa can appropriately be estimated.
CITATIONS LIST
Patent Literature
Patent Literature 1: Japanese Unexamined Patent Application
Publication No. 2003-048526
SUMMARY OF INVENTION
Technical Problems
An object of the present invention is to provide a four-wheel drive
vehicle in which a vehicle body speed is appropriately calculated
and an anti-skid control can be suitably executed.
Solutions to Problems
An anti-skid control device for a vehicle applied to a four wheel
drive vehicle in which a driving force from a driving source (PWU)
of the vehicle is transmitted to four wheels (WH[**]) according to
the present invention includes a wheel speed sensor (VWA[**]) that
detects wheel speeds (Vwa[**]) of four wheels (WH[**]) of the
vehicle; and a controller (ECU) that calculates a vehicle body
speed (Vxa) of the vehicle based on at least one of the four wheel
speeds (Vwa[**]) and executes an anti-skid control for suppressing
lock tendency of the four wheels (WH[**]) by selectively switching
between a reduction mode (Mgn) of reducing a braking torque applied
to the four wheels (WH[**]) and an increase mode (Mzo) of
increasing the braking torque based on a comparison result
(Slp[**]) between the four wheel speeds (Vwa[**]) and the vehicle
body speed (Vxa).
In the anti-skid control device for the vehicle according to the
present invention, the controller (ECU) calculates the
accelerations (dVw [**]) of the four wheels (WH [**]) based on the
four wheel speeds (Vwa [**]) and is configured to include a control
mode condition of selecting the reduction mode (Mgn) in the four
wheels (WH [**]) and a wheel acceleration condition in which the
accelerations (dVw [**]) of the four wheels (WH [**]) are within a
range of a predetermined value (dvx) (|dVw [**]|<dvx). The
controller determines as a residual state (FLzn=1) when a state in
which the control mode condition and the wheel acceleration
condition are satisfied at the same time is continued for a
predetermined time (tkx). The controller calculates the vehicle
body speed (Vxa) based on a maximum speed value (Vwa[**]d), which
is a maximum value of the four wheel speeds (Vwa[**]) when
determined as not the residual state (FLzn=0), and calculates the
vehicle body speed (Vxa) based on a minimum speed value (Vwa[**]s),
which is a minimum value of the four wheel speeds (Vwa[**]) when
determined as the residual state (FLzn=1).
In the anti-skid control device for the vehicle according to the
present invention, the controller (ECU) is configured to include a
control mode condition of selecting the reduction mode (Mgn) in the
four wheels (WH [**]) and a wheel speed condition in which a
difference (eVw) between the maximum speed value (Vwa[**]d) which
is the maximum value of the four wheel speeds (Vwa[**]) and the
minimum speed value (Vwa[**]s) which is the minimum value of the
four wheel speeds (Vwa[**]) is less than or equal to a
predetermined speed (vwx). The controller determines as the
residual state (FLzn=1) when a state in which the control mode
condition and the wheel speed condition are satisfied at the same
time is continued for the predetermined time (tkx). The controller
calculates the vehicle body speed (Vxa) based on the maximum speed
value (Vwa [**]d) when determined as not the residual state
(FLzn=0), and calculates the vehicle body speed (Vxa) based on the
minimum speed value (Vwa [**]s) when determined as the residual
state (FLzn=1).
When the wheel speed Vwa[**] includes the acceleration slip Sks,
the maximum value Vwa [**]d of the wheel speed is deviated the most
from the true value Vxs of the vehicle body speed, and the minimum
value Vwa [**]s of the wheel speed is the closest to the true value
Vxs. According to the above configuration, "whether or not in the
residual state" is determined based on each condition (control mode
condition etc.), where the vehicle body speed Vxa is calculated
based on the maximum value Vwa[**]d when not determined as the
residual state, and the vehicle body speed Vxa is calculated based
on the minimum value Vwa[**]s when determined as the residual
state. Therefore, when the wheel speed Vwa[**] includes the
acceleration slip Sks, the vehicle body speed Vxa is determined
with the influence of the acceleration slip Sks suppressed to a
minimum. As a result, anti-skid control is suitably executed, and
the vehicle can be reliably decelerated.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is an overall configuration view of a vehicle mounted with
an antiskid control device ASC for a vehicle in accordance with the
present invention.
FIG. 2 is a flowchart explaining a processing outline of the
anti-skid control.
FIG. 3 is a flowchart explaining a process of determining a control
state.
FIG. 4 is a time series diagram explaining problems, operations and
effects caused by the acceleration slip Sks.
DESCRIPTION OF EMBODIMENTS
<Explanation of Symbols>
In the following description, configuring members denoted with the
same reference symbols, calculation processes, signals,
characteristics, and values exhibit the same function. Therefore,
redundant explanation may be omitted.
The bracketed subscript [**] provided at the end of various symbols
indicates to which one of the four wheels in the front, rear, left
and right of the vehicle it relates to. Specifically, each
subscript corresponds to [fl] for the left front wheel, [fr] for
the right front wheel, [rl] for the left rear wheel, and [rr] for
the right rear wheel. In addition, the subscript [**] may be
omitted. For example, the wheel speed sensor VWA [**] (written as
"VWA" when subscript [**] is omitted) comprehensively indicates a
wheel speed sensor VWA [fl] for the front left wheel, a wheel speed
sensor VWA [fr] for the right front wheel, a wheel speed sensor VWA
[rl] for the left rear wheel, and a wheel speed sensor VWA [rr] for
the right rear wheel.
<Overall Structure of Anti-Skid Control Device for a Vehicle in
Accordance with the Present Invention>
An anti-skid control device ASC according to the present invention
will be described with reference to an overall configuration view
of FIG. 1. The vehicle is a four-wheel drive type vehicle in which
all four wheels are drive wheels (wheels to which driving force is
transmitted).
In a vehicle equipped with the anti-skid control device ASC, a
braking operation member BP, a braking operation amount sensor BPA,
a brake switch BSW, a controller ECU, a wheel speed sensor VWA
[**], and a brake actuator (also simply referred to as "actuator")
BRK are provided. Furthermore, a brake caliper CP [**], a wheel
cylinder WC [**], a rotating member KT [**], and a friction member
MS [**] are provided on the four wheels WH [**] of the vehicle. The
actuator BRK and the wheel cylinder WC [**] are connected through a
brake pipe HK [**].
The vehicle (so-called full time 4WD vehicle) includes a power
source (power unit) PWU that generates a driving force and a
transmission TRN connected to the power source PWU. That is, the
wheels WH [**] are always mechanically connected to the power
source PWU through the transmission TRN. For example, the power
source PWU is an internal combustion engine (so-called engine), an
electric motor. The output (driving force) of the power source PWU
is appropriately distributed and transmitted to the front wheels WH
[fl], WH [fr] and the rear wheels WH [rl], WH [rr] by the
transmission TRN. Here, the driving force is transmitted from the
transmission TRN to the side of the rear wheels WH [rl], WH [rr]
via a propeller shaft PPS.
The front wheel side driving force is transmitted to the left and
right front wheels WH [fr], WH [fl] through a front wheel
differential FDF and a front wheel drive shaft FDS, respectively.
The rear wheel side driving force is transmitted to the left and
right rear wheels WH [rr], WH [rl] through a rear wheel
differential RDF and a rear wheel drive shaft RDS, respectively.
Furthermore, the transmission TRN is provided with a center
differential CDF, and the front wheel side driving force and the
rear wheel side driving force can be appropriately adjusted
according to a traveling state of the vehicle. For example, viscous
coupling can be adopted as the center differential CDF.
The braking operation member (e.g., brake pedal) BP is a member
operated by a driver to decelerate the vehicle. A braking torque on
the wheel WH [**] (also simply referred to as "WH") is adjusted by
operating the braking operation member BP, and a braking force is
generated on the wheel WH. Specifically, a rotating member (e.g.,
brake disc) KT [**] is fixed to the wheel WH of the vehicle. A
brake caliper CP [**] (also simply referred to as "CP") is disposed
so as to sandwich the rotating member KT [**] (also simply referred
to as "KT").
A wheel cylinder WC [**] (also simply referred to as "WC") is
provided in the brake caliper (also simply referred to as caliper)
CP. As the hydraulic pressure in the wheel cylinder WC of the
caliper CP is adjusted (increased or reduced), the piston in the
wheel cylinder WC is moved (forward or backward) with respect to
the rotating member KT. This movement of the piston causes a
friction member (e.g., brake pad) MS [**] to be pressed against the
rotating member KT, thus generating a pressing force. The rotating
member KT and the wheel WH are fixed so as to rotate integrally.
Therefore, a braking torque (braking force) is generated in the
wheel WH by the frictional force generated by the pressing
force.
The braking operation member BP is provided with a braking
operation amount sensor (also simply referred to as "operation
amount sensor") BPA. The operation amount Bpa of the braking
operation member (brake pedal) BP by the driver is detected by the
operation amount sensor BPA. Specifically, as the braking operation
amount sensor BPA, at least one of a hydraulic pressure sensor that
detects the pressure of a master cylinder MC, an operation
displacement sensor that detects the operation displacement of the
braking operation member BP, and an operation force sensor that
detects the operation force of the braking operation member BP is
adopted.
In other words, the operation amount sensor BPA is a generic name
for the master cylinder hydraulic pressure sensor, the operation
displacement sensor, and the operation force sensor. Therefore, the
braking operation amount Bpa is determined based on at least one of
the hydraulic pressure of the master cylinder MC, the operation
displacement of the braking operation member BP, and the operation
force of the braking operation member BP. The operation amount Bpa
is input to a controller ECU.
In addition, a brake switch BSW is provided in the braking
operation member BP. The brake switch BSW is an ON/OFF switch that
detects whether or not the braking operation member BP is operated.
When the braking operation member BP is operated by the brake
switch BSW, an ON signal is transmitted to the controller ECU, and
when the braking operation member BP is not operated, an OFF signal
is transmitted.
The controller (also referred to as "electronic control unit") ECU
is configured by an electric circuit board on which a
microprocessor or the like is mounted and a control algorithm
programmed in the microprocessor. In the controller ECU, an
anti-skid control is executed based on the detection value (wheel
speed) Vwa [**] (also simply referred to as "Vwa") of the wheel
speed sensor VWA [**] (also simply referred to as "VWA").
Specifically, a slip state quantity Slp (also simply referred to as
"Slp") representing the slip degree of each wheel WH is calculated
based on the wheel speed Vwa. Then, based on the slip state
quantity Slp [**], a drive signal Cmd for adjusting the hydraulic
pressure in the wheel cylinder WC is formed and transmitted to an
actuator BRK to reduce the slip degree of each wheel (i.e.,
suppress excessive deceleration slip Sgn and prevent locking
tendency of wheel WH). Here, the drive signal Cmd includes "control
mode of reduction mode Mgn or increase mode Mzo", "duty ratio Dug,
Duz of electromagnetic valve SV", and "drive instruction of
electric motor MT".
Each of the wheels WH of the vehicle is provided with a wheel speed
sensor VWA. Four wheel speeds Vwa are detected by the four wheel
speed sensors VWA. The wheel speed Vwa is input to the controller
ECU.
The brake fluid pressure of the wheel cylinder WC is generated by
the brake actuator (also simply referred to as "actuator") BRK in
accordance with the operation of the braking operation member BP.
In addition, when the anti-skid control is executed, the brake
fluid pressure of the wheel cylinder WC is adjusted (increased or
reduced) by the actuator BRK. The actuator BRK is configured by the
master cylinder MC for generating a brake fluid pressure
corresponding to the operation force of the brake pedal BP and a
hydraulic unit HU capable of independently adjusting the brake
fluid pressure to be supplied to each wheel cylinder WC. The
configurations of the master cylinder MC and the hydraulic unit HU
are well known and therefore will be briefly described.
The master cylinder MC is mechanically connected to the braking
operation member BP through a brake rod BRD. The operation force
(brake pedal pressing force) of the braking operation member BP is
converted into the pressure of the brake fluid by the master
cylinder MC.
The hydraulic unit HU is provided between the master cylinder MC
and each wheel cylinder WC. When the anti-skid control is executed,
the hydraulic unit HU adjusts the brake fluid pressure Pw [**] of
each wheel cylinder WC [**] independently for each wheel. The
hydraulic unit HU is configured by a plurality of electromagnetic
valves SV (e.g., two position electromagnetic valves of ON/OFF), a
low pressure reservoir RV, a hydraulic pump HP, and an electric
motor MT.
In a case where the brake fluid pressure Pw [**] needs to be
reduced by the anti-skid control (referred to as "reduction mode
Mgn"), the normally open type pressure increasing valve of the
electromagnetic valves SV is closed and the normally closed type
pressure reducing valve of the electromagnetic valves SV is opened.
Since the brake fluid in the wheel cylinder WC is moved to the low
pressure reservoir RV, the brake fluid pressure of the wheel
cylinder WC is reduced. Here, the pressure reducing speed (time
gradient in reducing of brake fluid pressure) is determined by a
duty ratio of the pressure reducing valve (time ratio of energized
state in constant period) Dug. Specifically, the duty ratio Dug
"100%" always corresponds to the open state, and the brake fluid
pressure is rapidly reduced. The duty ratio Dug "0%" always
corresponds to the closed state.
In a case where the brake fluid pressure Pw [**] needs to be
increased by the anti-skid control (referred to as "increase mode
Mzo"), the pressure increasing valve of the electromagnetic valves
SV is opened and the pressure reducing valve of the electromagnetic
valves SV is closed. Then, the brake fluid is moved from the master
cylinder MC to the wheel cylinder WC, and the brake fluid pressure
of the wheel cylinder WC is increased. Here, the pressure
increasing speed (time gradient in increasing of brake fluid
pressure) is determined by a duty ratio of the pressure increasing
valve (time ratio of energized state in constant period) Duz.
Specifically, the duty ratio Duz "0%" always corresponds to the
open state and the brake fluid pressure is rapidly increased. The
duty ratio Duz "100%" always corresponds to the closed state.
In the reduction mode Mgn, the brake fluid accumulated in the low
pressure reservoir RV is returned to the fluid path between the
pressure increasing valve of the electromagnetic valve SV and the
master cylinder MC by the hydraulic pump HP driven by the electric
motor MT. The electromagnetic valve SV (pressure increasing valve,
pressure reducing valve) and the electric motor MT are driven
(controlled) by the drive signal Cmd.
In a case where the brake fluid pressure needs to be held by the
anti-skid control, the pressure reducing valve or the pressure
increasing valve of the electromagnetic valve SV is always closed
in the reduction mode Mgn or the increase mode Mzo. More
specifically, in a case where the brake fluid pressure needs to be
held in the reduction mode Mgn, the duty ratio Dug of the pressure
reducing valve is determined to be "0% (normally closed state)" by
the drive signal Cmd. Furthermore, in a case where the brake fluid
pressure needs to be held in the increase mode Mzo, the duty ratio
Duz of the pressure increasing valve is determined to be "100%
(normally closed state)" by the drive signal Cmd.
<Processing Outline of Anti-Skid Control>
With reference to the flowchart of FIG. 2, an outline of the
overall processing of the anti-skid control (control to reduce
excessive slip of the wheel and suppress the locking tendency of
the wheel) will be described. The processing of the anti-skid
control is programmed in the microprocessor in the controller
ECU.
In the anti-skid control, the vehicle body speed Vxa is estimated
based on at least one of the four wheel speeds Vwa. Then, the brake
fluid pressure of the wheel cylinder WC is adjusted based on a
comparison between the wheel speed Vwa and the vehicle body speed
Vxa. Adjustment of the brake fluid pressure is achieved by
selecting one of the reduction mode (pressure reducing mode) Mgn
and the increase mode (pressure increasing mode) Mzo. Here, the
reduction mode Mgn and the increase mode Mzo are collectively
referred to as "control mode".
In step S110, the braking operation amount Bpa, the brake switch
signal Bsw, the wheel speed Vwa [**], and the drive signal Cmd are
read. The braking operation amount Bpa is a signal from the braking
operation amount sensor BPA and the signal Bsw is a signal from the
brake switch BSW. Furthermore, the wheel speed Vwa is detected by
the wheel speed sensor VWA provided in the wheel WH. The drive
signal Cmd is a drive signal processed in the controller ECU, and
includes information such as a control mode (selection result from
reduction mode Mgn and increase mode Mzo), a duty ratio (target
value) Dug, Duz of the electromagnetic valve SV and the like.
In step S120, "whether or not the vehicle is braking" is determined
based on at least one of the braking operation amount Bpa and the
switch signal Bsw. For example, determination is made that the
vehicle is braking when the operation amount Bpa is greater than or
equal to a predetermined value bp0, and determination is made that
the vehicle is not braking when the operation amount Bpa is less
than the predetermined value bp0. Here, the predetermined value bp0
is a threshold value for determination set in advance and
corresponds to "play" of the braking operation member (brake pedal)
BP. Furthermore, determination is made that the vehicle is braking
when the switch signal Bsw indicates the ON state (ON signal), and
determination is made that the vehicle is not braking when the
switch signal Bsw indicates the OFF state (OFF signal).
When the vehicle is not performing the braking operation and the
determination of step S120 is negative (if "NO"), the process
returns to step S110. When the vehicle is performing the braking
operation and the determination of step S120 is affirmative (if
"YES"), the process proceeds to step S130.
In step S130, the wheel acceleration (time change amount of wheel
speed) dVw [**] is calculated based on the wheel speed Vwa [**] of
each wheel WH [**]. Specifically, the wheel acceleration dVw [**]
(also simply referred to as "dVw") is calculated by time
differentiating the wheel speed Vwa [**]. Here, the wheel
acceleration dVw is calculated as a value having a positive (plus)
sign when the rotational movement of the wheel WH is accelerating,
and a negative (minus) sign when the rotational movement of the
wheel WH is decelerating.
In step S140, the control state is determined based on at least one
of the wheel speed Vwa and the wheel acceleration dVw. The "control
state" includes "residual state" and "normal state" which is not
the residual state. The residual state corresponds to a state in
which "the influence of the acceleration slip Sks remains in the
wheel speed Vwa [**], but the wheel speed Vwa [**] is converging
toward the true value Vxs of the vehicle body speed". Furthermore,
the normal state corresponds to a state in which the influence of
the acceleration slip Sks does not exist in the wheel speed Vwa
[**].
In step S140, when the normal state (state in which the residual
state is denied) is determined as the control state, a control flag
(determination flag) FLzn is set to "0" to display this. On the
other hand, when the residual state is determined as the control
state, the control flag FLzn is set to "1". The control state is
set to the normal state (i.e., FLzn=0) as the initial state
(default). A detailed method of determining the control state will
be described later.
In step S150, the vehicle body speed Vxa is calculated based on the
control state. More specifically, when the control state is the
normal state (FLzn=0), the vehicle body speed Vxa is calculated
based on the maximum speed value Vwa [**]d. Here, the "maximum
speed value Vwa [**]d" is the largest value (i.e., fastest) among
the wheel speeds Vwa [**] of the four wheels WH [**]. The subscript
"d" after the bracket indicates the "maximum value" among a
plurality of corresponding wheel speeds (e.g., wheel speed Vwa
[**]).
On the other hand, when the control state is the residual state
(FLzn=1), the vehicle body speed Vxa is calculated based on a
minimum speed value Vwa [**]s. Here, the "minimum speed value Vwa
[**]s" is the smallest value (i.e., slowest) among the wheel speeds
Vwa [**] of the four wheels WH [**]. The subscript "s" after the
bracket indicates the "minimum value" among a plurality of
corresponding wheel speeds (e.g., wheel speed Vwa [**]).
Furthermore, when the vehicle body speed Vxa is calculated, a
limitation is provided in the time change amount of the vehicle
body speed Vxa. That is, the upper limit value .alpha.up of the
increasing gradient and the lower limit value .alpha.dn of the
decreasing gradient of the vehicle body speed Vxa are set, and the
change in the vehicle body speed Vxa is restricted by the upper and
lower limits .alpha.up, .alpha.dn. This is because the inertia of
the entire vehicle is very large and is less likely to change as
compared with the inertia of the wheel WH.
For example, when determination is made that the vehicle is in the
normal state (i.e., not residual state) and the limitations of the
upper and lower limit values .alpha.up, .alpha.dn of the change
gradient are not received, the maximum speed value Vwa [**]d is
calculated as it is as the vehicle body speed Vxa. On the other
hand, when receiving the limitations of upper and lower limit
values .alpha.up, .alpha.dn, the maximum speed value Vwa [**]d is
limited by the upper and lower limit values .alpha.up, .alpha.dn,
and the vehicle body speed Vxa is calculated.
Furthermore, when determination is made that the vehicle is in the
residual state and the limitations of the upper and lower limit
values .alpha.up and .alpha.dn of the change gradient are not
received, the minimum speed value Vwa [**]s is determined as the
vehicle body speed Vxa as is. On the other hand, when receiving the
limitations of the upper and lower limit values .alpha.up,
.alpha.dn, the minimum speed value Vwa [**]s is limited by the
upper and lower limit values .alpha.up, .alpha.dn, and the vehicle
body speed Vxa is calculated. After the vehicle body speed Vxa is
determined in step S150, the process proceeds to step S160.
In step S160, the slip state quantity Slp [**] of the wheel WH [**]
is calculated based on the comparison between the vehicle body
speed Vxa and the wheel speed Vwa [**]. Here, the slip state
quantity Slp [**] (also simply referred to as "Slp") is a state
quantity (variable) representing the slip degree of the wheel WH.
For example, a slip speed which is a deviation of the vehicle body
speed Vxa and the wheel speed Vwa is adopted as the slip state
quantity Slp (Slp [**]=Vxa-Vwa [**]). Furthermore, the slip speed
is made dimensionless by the vehicle body speed Vxa to calculate
the slip rate (=Slp [**]/Vxa), and the slip rate can be adopted as
the slip state quantity Slp [**].
In step S170, the anti-skid control is executed based on the wheel
acceleration dVw [**] and the slip state quantity Slp [**].
Specifically, in each control mode of the anti-skid control, a
plurality of threshold values are set in advance. Either one of the
control modes, the reduction mode Mgn or the increase mode Mzo, is
selected based on the correlation between these threshold values
and "the wheel acceleration dVw [**] and the slip state quantity
Slp [**]". In addition, the duty ratio Dug of the pressure reducing
valve and the duty ratio Duz of the pressure increasing valve are
determined. Then, the electromagnetic valve SV is driven and the
brake fluid pressure of the wheel cylinder WC is adjusted on the
basis of the selected control mode and the determined duty ratio.
In addition, in order to reflux the brake fluid from the low
pressure reservoir RV, a drive signal of the electric motor MT is
formed.
<Process of Determining Control State>
With reference to the flowchart of FIG. 3, the process of
determining the control state in step S140 will be described. As
described above, the control state includes two states (normal
state and residual state). Each state is represented by a control
flag (also referred to as a determination flag) FLzn. Specifically,
"FLzn=0" is displayed in the normal state, and "FLzn=1" is
displayed in the residual state.
In step S210, "whether or not the control state is the residual
state" is determined based on the control state (i.e., control flag
FLzn) in the previous calculation cycle. When "FLzn=0" and the
result of step S210 is negative (if "NO"), the process proceeds to
step S220. On the other hand, when "FLzn=1" and the result of step
S210 is affirmative (if "YES"), the process proceeds to step S230.
As the initial value, the control flag FLzn is set to "0".
In step S220, "whether or not the start condition of the residual
state is satisfied" is determined based on the control mode of the
wheel WH [**], the wheel speed Vwa [**], and the wheel acceleration
dVw [**]. Specifically, when a state in which the following three
conditions (1) to (3) are satisfied at the same time is continued
for a predetermined duration tkx (corresponding to "predetermined
time"), the start of the residual state is determined. Here, the
predetermined duration tkx is a threshold value for time lapse
determination, and is a predetermined value set in advance.
(1) In all four wheels WH [**], the reduction mode Mgn is selected.
This condition is called "control mode condition".
(2) The wheel acceleration dVw [**] is within a range of a
predetermined wheel acceleration dvx. In other words, the absolute
value of the wheel acceleration dVw [**] is less than or equal to
the predetermined wheel acceleration dvx. That is, "|dVw [**]| dvx"
is satisfied. Here, the predetermined wheel acceleration dvx is a
threshold value for start determination, and is a predetermined
value set in advance. The predetermined wheel acceleration dvx is a
value larger than "0". This condition is called "wheel acceleration
condition".
(3) The difference eVw between the maximum value (maximum speed
value) Vwa [**]d of the four wheel speeds Vwa [**] and the minimum
value (minimum speed value) Vwa [**]s of the four wheel speeds Vwa
[**] is less than or equal to a predetermined speed vwy. That is,
"Vwa [**]d-Vwa [**]s (=eVw).ltoreq.vwy" is satisfied. Here, the
predetermined speed vwy is a threshold value for start
determination, and is a predetermined value set in advance. As
described above, the subscript "d" after the bracket indicates the
"maximum value" of the corresponding plurality of signals, and the
subscript "s" after the bracket indicates the "minimum value" of
the corresponding plurality of signals. This condition is called
"wheel speed condition".
When the start condition of the residual state is satisfied and the
result of step S220 is affirmative (if "YES"), the process proceeds
to step S240. Here, the calculation cycle in which the affirmative
determination is made in step S220 is the starting time point of
the residual state. On the other hand, when the start condition of
the residual state is not satisfied and the result of step S220 is
negative (if "NO"), the process proceeds to step S250.
In step S230, "whether or not the end condition of the residual
state is satisfied" is determined based on the duration Tkz of the
residual state. Specifically, when the duration Tkz is greater than
or equal to the predetermined residual time tzn, the end of the
residual state is determined. Therefore, when the duration Tkz is
less than the predetermined residual time tzn, the end of the
residual state is not determined and the residual state is
continued. That is, the control state is switched from the residual
state to the normal state at the time point (calculation cycle) the
duration Tkz coincides with the predetermined residual time tzn.
Here, the predetermined residual time tzn is a threshold for end
determination and is a predetermined value set in advance.
When the end condition of the residual state is satisfied and the
result of step S230 is affirmative (if "YES"), the process proceeds
to step S260. Here, the calculation cycle in which the affirmative
determination is made in step S230 is the terminating time point of
the residual state. On the other hand, when the end condition of
the residual state is not satisfied and the result of step S230 is
negative (if "NO"), the process proceeds to step S270.
In step S240, the residual state is started. Specifically, the
control state is switched from the normal state to the residual
state. The control flag FLzn is switched from "0" to "1" at the
starting time point (calculation cycle) of the residual state.
In step S250, the residual state is not started, and the control
state is maintained in the normal state. That is, the control flag
FLzn remains "0".
In step S260, the residual state is ended. Specifically, the
control state is switched from the residual state to the normal
state. At the terminating time point of the residual state
(calculation cycle), the control flag FLzn is switched from "0" to
"1".
In step S270, the residual state is not ended and the control state
is maintained in the residual state. That is, the control flag FLzn
remains "1".
In the processes from step S240 to step S270, the control state
(i.e., control flag FLzn) is set, and the process proceeds to step
S150. In step S150, when the control flag FLzn is "0" (when
determined as not the residual state), the vehicle body speed Vxa
is calculated based on the maximum speed value Vwa [**]d. On the
other hand, when the control flag FLzn is "1" (when determined as
the residual state), the vehicle body speed Vxa is calculated based
on the minimum speed value Vwa [**]s.
<<Starting Process and Terminating Process of Residual
State>>
The meaning of the starting process and the terminating process of
the residual state will be described. On the assumption of the (1)
control mode condition, it is determined that the braking torque
and the road surface reactive force are approaching an equilibrium
state (or are already in equilibrium state) by the (2) wheel
acceleration condition. This is based on a phenomenon that "when
the braking torque and the reactive force from the road surface are
approaching an equilibrium state, the absolute value of the wheel
acceleration dVw decreases". That is, since the braking torque is
not increased in the reduction mode Mgn, if all the wheel
accelerations dVw [**] are within the range of the predetermined
wheel acceleration dvx, the state is not a state in which all the
wheel speeds Vwa [**] are rapidly changing but is converging toward
the true value Vxs of the vehicle body speed or has been converged
to some extent.
Similarly, on the assumption of the (1) control mode condition, it
is determined that the braking torque and the road surface reactive
force are approaching an equilibrium state (or are already in
equilibrium state) by the (3) wheel speed condition. Since the
braking torque is not increased in the reduction mode Mgn, if all
the wheel speeds Vwa [**] are within the predetermined speed vwy,
the state is not a state in which all the wheel speeds Vwa [**] are
rapidly changing but is converging toward the true value Vxs of the
vehicle body speed or is converged to some extent.
Therefore, at a time point the state in which all the above three
conditions are satisfied continued for the predetermined duration
tkx, the control state is switched from the normal state to the
residual state (i.e., residual state is started). When the wheel
speed Vwa includes the acceleration slip Sks, the maximum speed
value Vwa [**]d is deviated the most from the true value Vxs of the
vehicle body speed, and the minimum speed value Vwa [**]s is the
closest to the true value Vxs. Thus, the minimum speed value Vwa
[**]s is adopted instead of the maximum speed value Vwa [**]d for
the calculation of the vehicle body speed Vxa. As a result, the
influence of the acceleration slip Sks is suppressed to a
minimum.
Under the above-described start condition, a convergence state of a
certain extent of the wheel speed Vwa [**] is determined based on
the combination of "the control mode condition and the wheel
acceleration condition" (referred to as "first group condition")
and the combination of "the control mode condition and the wheel
speed condition" (referred to as "second group condition"). A more
reliable determination of the start of the residual state can be
achieved by the two group conditions (first and second group
conditions). However, one of the two group conditions can be
omitted. That is, any one of the following three cases can be
adopted as the start condition.
(A) When a state in which the two conditions of the control mode
condition and the wheel acceleration condition are simultaneously
satisfied is continued for the predetermined duration tkx (first
group condition)
(B) When a state in which the two conditions of the control mode
condition and wheel speed condition are simultaneously satisfied is
continued for the predetermined duration tkx (second group
condition)
(C) When a state in which the three conditions of the control mode
condition, the wheel speed condition, and the wheel acceleration
condition are simultaneously satisfied is continued for the
predetermined duration tkx (first group condition+second group
condition)
While the anti-skid control is being executed, the driver's
acceleration operation has already been terminated. Therefore, the
influence of the acceleration slip Sks at the wheel speed Vwa [**]
is not continued for a long time. Therefore, when the duration Tkz
of the residual state becomes greater than or equal to the
predetermined residual time tzn, the residual state is ended and
the state is returned to the normal state. The meaning of the
starting process and the terminating process of the residual state
has been described above.
<Operation/Effect>
With reference to the time series diagram of FIG. 4, the operation
and effect of the ASC for the vehicle according to the present
invention will be described. A case where sudden braking is
performed immediately after the vehicle is rapidly accelerated, and
the antiskid control is executed is assumed. As described above,
the subscript [**] at the end of the reference symbol is the
inclusive sign of each wheel. The subscript [**] may be
omitted.
The vehicle is rapidly accelerated until time point t0, and the
acceleration slip Sks is generated in the four wheels WH [**]. At
time point t0, the acceleration operation is terminated, and at
time point t1 immediately thereafter, the braking operation is
started, and at time point t2, the anti-skid control is started.
Since each wheel WH [**] is always (i.e., even at time of braking)
mechanically connected to the power source PWU, the influence of
acceleration still remains even if the braking operation is
started.
From time point t2 to time point t3, the start condition of the
residual state is not satisfied. Therefore, the control state
remains in the normal state (FLzn=0) which is the initial state.
Therefore, the vehicle body speed Vxa is calculated based on the
maximum speed value Vwa [**]d.
At time point t3, the start condition of the residual state is
satisfied. Specifically, a state in which "all of the four wheels
WH [**] are in the reduction mode Mgn (control mode condition)" and
"the four wheel accelerations dVw [**] are within a range of the
predetermined wheel acceleration dvx (|dVw [**]|.ltoreq.dvx) (wheel
acceleration condition)" and the difference eVw between the maximum
speed value Vwa [**]d and the minimum speed value Vwa [**]s is
smaller than or equal to the predetermined speed vwy (Vwa [**]d-Vwa
[**]s vwy) (wheel speed condition) "is continued for the
predetermined duration tkx. In other words, as the start condition,
"a state in which the above three conditions (1) to (3) are
satisfied at the same time is continued for the predetermined
duration tkx" is adopted. The predetermined wheel acceleration dvx
and the predetermined duration tkx (corresponds to "predetermined
time") are threshold values for start determination, and are
predetermined values set in advance.
Then, at time point t3, the control state is transitioned from the
normal state (FLzn=0) to the residual state (FLzn=1). Thus, the
vehicle body speed Vxa is calculated based on the minimum speed
value Vwa [**]d (slowest of four wheel speeds Vwa [**]) instead of
the maximum speed value Vwa[**]d (fastest if four wheel speeds Vwa.
In the situation where the acceleration slip Sks remains, the
minimum speed value Vwa [**]s is the closest to the vehicle body
speed true value Vxs. The slip state quantity Slp is appropriately
calculated by calculating the vehicle body speed Vxa based on the
minimum speed value Vwa [**]s. As a result, the control mode (in
particular, the reduction mode Mgn) is appropriately selected and
the vehicle can be reliably decelerated.
At time point t4, the end condition of the residual state is
satisfied. Specifically, the duration Tkz of the residual state
counted for time from the time point t3 reaches the predetermined
residual time tzn. At time point t4, the control state is
transitioned from the residual state (FLzn=1) to the normal state
(FLzn=0). As a result, the vehicle body speed Vxa is calculated
based on the maximum speed value Vwa [**]d instead of the minimum
speed value Vwa [**]s.
Since the influence of the acceleration slip Sks is not continued
for a long time, the wheel speed Vwa [**] does not include the
acceleration slip Sks before reaching time point t4, and the
deceleration slip Sgn is generated. Therefore, it is returned to
the method based on the maximum speed value Vwa [**]d which is the
normal calculation method of the vehicle body speed Vxa.
As described above, in the start condition of the residual state,
any one of the wheel acceleration condition and the wheel speed
condition can be omitted. This is because both of these two
conditions indicate that "all the wheel speeds Vwa [**] are
converging towards the true value Vxs of the vehicle body speed or
are converged to a certain extent",
Other Embodiments
Other embodiments will be described below. Even in the other
embodiments, effects similar to above (reduction of influence of
acceleration slip in calculation of vehicle body speed Vxa) are
achieved.
In the embodiment described above, the configuration of the disc
type braking device (disc brake) has been exemplified. In this
case, the friction member MS is a brake pad and the rotating member
KT is a brake disc. Instead of the disc type braking device, a drum
type braking device (drum brake) can be adopted. In the case of a
drum brake, a brake drum is adopted instead of the caliper CP.
Furthermore, the friction member MS is a brake shoe and the
rotating member KT is a brake drum.
In the embodiment described above, a hydraulic type using the brake
fluid has been exemplified as a device for applying the braking
torque to the wheel WH. Instead, an electrical type driven by an
electric motor may be adopted. In the electrical device, the
rotational power of the electric motor is converted into a linear
power, whereby the friction member MS is pressed against the
rotating member KT. Therefore, the braking torque is directly
generated by the electric motor without depending on the pressure
of the brake fluid. Furthermore, a composite type configuration in
which a hydraulic type using a brake fluid is adopted for the front
wheel, and an electrical type is adopted for the rear wheel can be
formed.
The influence of the acceleration slip Sks appears immediately
after the start of the anti-skid control. Therefore, the starting
process of the residual state can be limited to within a
predetermined time tst after the start of the anti-skid control.
Specifically, the start determination of the residual state
(process of step S220) is permitted until the predetermined time
tst has elapsed from the starting time point of the anti-skid
control. However, after the predetermined time tst has elapsed, the
start determination process can be prohibited. The predetermined
time tst is a threshold value for the limit determination and is a
predetermined value set in advance.
Instead of the predetermined time tst described above, the number
of reduction modes Mgn may be adopted. That is, in the reduction
mode Mgn up to the nth time after the start of the antiskid
control, the start determination of the residual state (process of
step S220) is permitted. However, in the reduction mode Mgn after
the (n+1)th time, the start determination processing is prohibited.
Here, "n" is a predetermined number of times (predetermined
positive integer), and for example, may be set as "n=1".
Furthermore, the acceleration state quantity of the vehicle is
detected, and whether or not the start determination of the
residual state is required can be determined based thereon.
Specifically, when the acceleration state quantity is greater than
or equal to the predetermined value, the process of determining the
start of the residual state is executed, but when the acceleration
state quantity is less than the predetermined value, the process of
determining the start of the residual state can be prohibited. The
acceleration state quantity can be calculated by at least one of
the operation amount of the acceleration operation member
(accelerator pedal), the throttle opening degree of the power
source PWU (internal combustion engine), the injection amount, and
the current flowing amount of the power source PWU (drive
motor).
* * * * *